The present embodiments relate to semiconductor circuits and are more particularly directed to a Schottky diode formed in part with a spike implant.
Semiconductor devices are prevalent in all aspects of electronic circuits, and various materials are used in the creation of such devices. For example, deep sub-micron technology (e.g., gate width of 0.5 micron or less) uses metal silicide, that is, a metal reacted with silicon, for various devices. For example, silicide ohmic contacts are used to reduce gate and source and drain contact resistance. As other examples, silcides may be used in connection with polysilicon resistors and capacitors. In the method steps of forming such devices (the “method flow”), therefore, often a particular metal is selected to form these silcides. In a common application, a metal such as titanium (Ti), cobalt (Co), nickel (Ni), or molybdenum (Mo) may be so chosen, thereby forming a respective silicide of TiSi2, CoSi2, NiSi, or MoSi.
While the above-discussed metals prove workable in various applications, they may not be optimal in connection with the formation of a particular and known semiconductor circuit element, the Schottky diode. A Schottky diode typically includes a metal to lightly-doped semiconductor interface, where this interface is known to have rectifying characteristics. Thus, for this interface, an appropriate metal should be selected. However, the metal selection contributes to the barrier height of the diode, and that barrier height may be critical for certain applications. Particularly, the above-introduced common metals of Ti, Co, Ni, and alternative metals of Pt and Pd typically provide a medium (Ti) or higher (Co, Ni) or very high barrier height (PtSi Pd2Si) Schottky diode on N-type doped silicon. Thus, in a method flow where a very low low barrier height Schottky diode is desired, while one of the common metals of Ti, Co, and Ni may be used with other devices formed as part of the same overall method flow, an alternative metal may be required to form the Schottky diode so as to provide the desired barrier height. Such alternative metals include, by ways of example, platinum (Pt) and palladium (Pd), which therefore form a respective silicide of PtSi or Pd2Si on P-type doped silicon for very low barrier height diodes or on N-type doped silicon for very high barrier height Schottky diodes.
By way of further background, various applications now require or benefit from the use of low barrier height Schottky diodes. For example, one such application is the implementation of radio frequency identification (“RFID”) passive tag devices. An RFID device, as known in that art, is a device that receives a radio frequency (“RF”) signal and provides a corresponding current in response to that signal. In some applications, the RFID device will receive a relatively small RF signal and, hence, in these applications a low-barrier Schottky diode is desirable so as to detect the small RF signal.
Given the preceding, one manner according to the prior art of creating a low barrier height Schottky diode for an application, such as RFID, is to use a P type material at the metal/semiconductor interface. However, if additional barrier lowering is needed, then two different silicides may be included in the method flow of the entire semiconductor structure, with a certain metal (e.g., Ti, Co, Ni) used for devices other than the Schottky diode(s) and a different metal (e.g., Pt, Pa) used for the low barrier Schottky diode(s). However, such an approach is very costly and, thus, may be undesirable or unacceptable.
Thus, there arises a need to address the drawbacks of the prior art, as is achieved by the preferred embodiments described below.